net/mlx5: modify ext-counter memory allocation

net/mlx5: modify ext-counter memory allocation

Currently, the counter pool needs 512 ext-counter memory for no batch
counters, it's allocated separately by once, behind the 512
basic-counter memory. This is not easy to get ext-counter pointer by
corresponding basic-counter pointer. This is also no easy for expanding
some other potential additional type of counter memory.

So, need allocate every one of ext-counter and basic-counter together,
as a single piece of memory. It's will be same for further additional
type of counter memory. In this case, one piece of memory contains all
type of memory for one counter, it's easy to get each type memory by
using offsetting.

Signed-off-by: Dong Zhou <dongz@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>